Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.49	12.634%	$59.1216	$59.12	$59.10	$59.10
Purchase #2	$150.73	7.836%	$162.5412	$162.54	$162.55	$162.50
Purchase #3	$15.96	12.845%	$18.0101	$18.01	$18.00	$18.00
Purchase #4	$172.51	8.654%	$187.439	$187.44	$187.45	$187.40
Purchase #5	$217.79	12.568%	$245.1618	$245.16	$245.15	$245.20
Purchase #6	$109.63	7.142%	$117.4598	$117.46	$117.45	$117.50
Purchase #7	$138.48	3.384%	$143.1662	$143.17	$143.15	$143.20
7 purchase totals =	$857.59		$932.8997	$932.90	$932.85	$932.90